Surfactants or surface active agents are generally described as any compound that reduces surface tension when dissolved in a solution (e.g., water) or that reduces interfacial tension between two liquids or between a liquid and a solid. An additive is defined herein as any compound that when added to a base hydraulic fluid improves the erosion performance of that hydraulic fluid. The choice of surfactant/additive varies with the application, system, or solution where it is employed. Some factors that are considered when evaluating the utility of a surfactant/additive include: solubility of the surfactant/additive in the system used, pH, ultimate surface tension required for spreading and/or for leveling, how corrosive the system components are, conductivity required, and volatility of the surfactant.
Surfactants are used in a variety of applications including aqueous and non-aqueous (i.e., organic) solutions. Applications that involve an extreme or a harsh environment include, but are not limited to, etching solutions used in preparation of semiconductor devices, electrochemical plating and polishing solutions, wafer cleaning and polishing solutions, anisotropic etching solutions, electrolytes for alkaline batteries, and developer solutions for semiconductor manufacture. An “extreme” or “harsh” environment is defined as an application where a conventional hydrocarbon-based surfactant/additive would be degraded. Degradation is defined herein as protonation of an anionic surfactant or degradation or alteration (e.g., polymerization) of the chemical structure of the surfactant that results in a change in surface tension and thus diminished surfactant performance.
Extreme environment conditions for aqueous solutions include, but are not restricted to, heat, light, radiation, oxidizing/reducing potential, high pressure, high shear, high or low pH, or the presence of corrosive reagents. The pH is generally low (i.e., acidic) or high (i.e., basic). Typically, for aqueous solutions, these applications are minimally both extreme in pH and corrosive.
Extreme environment conditions for non-aqueous solutions include, but are not restricted to, high pressure, high temperature (i.e., at least 200° C.), high shear, environmental (trace water), or corrosive reagents, etc.
Under these conditions, most hydrocarbon surfactants either chemically or physically degrade. Thus, non-hydrocarbon-based surfactants that do not degrade in extreme environments are desirable.
Fluorocarbon surfactants such as, perfluorooctanesulfonyl fluoride (POSF) derived surfactants like K+−OSO2C8F17 have been used. But these surfactants persist or ultimately degrade in the environment to other perfluorooctyl-containing compounds. It has been reported that certain perfluorooctyl-containing compounds may tend to have low bioelimination rates in living organisms. This tendency has been cited as a potential concern for some fluorochemical compounds. See, for example, U.S. Pat. No. 5,688,884 (Baker et al.). Introduction of a surfactant and its degradation products into the environment may occur either from streams related to the use of the surfactant itself or to waste streams/emissions from its manufacture.
As a result, there is a desire for fluorine-containing compositions that are effective in providing desired surfactant properties, and that eliminate more rapidly from the body (including the composition and its degradation products).
Therefore, the need exists for a surfactant or an additive that works effectively in an extreme environment application, that more rapidly eliminates from living organisms, and that can be manufactured in a cost effective manner. The precursor to these surfactants needs to be less bioaccumulative than POSF derived materials to prevent potentially introducing bioaccumulative materials from manufacturing streams.